Visible Light Photolysis of Hydrogen Iodide Using Sensitized Layered Semiconductor Particles

Surface sensitization of internally platinized layered oxide semiconductors K_4−xH_xNb₆O₁₇·nH₂O (x ≈ 2.5), H₂Ti₃O₇, and HTiNb0₅ by RuL₃²⁺ (L = 4,4′-dicarboxy-2,2′-bipyridine) yields photocatalysts for the production of H₂ and I₃⁻ in aqueous iodide solutions. Flash photolysis experiments show that, at pH 3.0, excited-state RuL₃²⁺ injects an electron into K_4−xH_xNb₆O₁₇·nH₂O and is rapidly re-reduced by I⁻. Steady-state photolysis at 450 nm in 50 mM aqueous KI (pH 3.0) yields H₂ and I₃⁻ in stoichiometric amounts, with an initial quantum yield of 0.3%. While H₂ and I₃⁻, once formed, do not recombine at an observable rate, the rate of hydrogen evolution decreases as the concentration of 1₃⁻ increases in the solution.